On 5/19/23 14:39, Johannes Weiner wrote:
> The different branches for retry are unnecessarily complicated. There
> are really only three outcomes: progress (retry n times), skipped
> (retry if reclaim can help), failed (retry with higher priority).
>
> Rearrange the branches and the retry counter to make it simpler.
>
> v2:
> - fix trace point build (Mel)
> - fix max_retries logic for costly allocs (Huang)
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> ---
> mm/page_alloc.c | 53 +++++++++++++++----------------------------------
> 1 file changed, 16 insertions(+), 37 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5a84a0bebc37..72660e924b95 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3772,16 +3772,22 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
> * Compaction managed to coalesce some page blocks, but the
> * allocation failed presumably due to a race. Retry some.
> */
> - if (compact_result == COMPACT_SUCCESS)
> - (*compaction_retries)++;
> + if (compact_result == COMPACT_SUCCESS) {
> + /*
> + * !costly requests are much more important than
> + * __GFP_RETRY_MAYFAIL costly ones because they are de
> + * facto nofail and invoke OOM killer to move on while
> + * costly can fail and users are ready to cope with
> + * that. 1/4 retries is rather arbitrary but we would
> + * need much more detailed feedback from compaction to
> + * make a better decision.
> + */
> + if (order > PAGE_ALLOC_COSTLY_ORDER)
> + max_retries /= 4;
>
> - /*
> - * All zones were scanned completely and still no result. It
> - * doesn't really make much sense to retry except when the
> - * failure could be caused by insufficient priority
> - */
> - if (compact_result == COMPACT_COMPLETE)
> - goto check_priority;
> + ret = ++(*compaction_retries) <= max_retries;
> + goto out;
I think you simplified this part too much, so now once it runs out of
retries, it will return false, while previously it would increase the priority.
> + }
>
> /*
> * Compaction was skipped due to a lack of free order-0
> @@ -3793,35 +3799,8 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
> }
>
> /*
> - * If compaction backed due to being deferred, due to
> - * contended locks in async mode, or due to scanners meeting
> - * after a partial scan, retry with increased priority.
> - */
> - if (compact_result == COMPACT_DEFERRED ||
> - compact_result == COMPACT_CONTENDED ||
> - compact_result == COMPACT_PARTIAL_SKIPPED)
> - goto check_priority;
> -
> - /*
> - * !costly requests are much more important than __GFP_RETRY_MAYFAIL
> - * costly ones because they are de facto nofail and invoke OOM
> - * killer to move on while costly can fail and users are ready
> - * to cope with that. 1/4 retries is rather arbitrary but we
> - * would need much more detailed feedback from compaction to
> - * make a better decision.
> - */
> - if (order > PAGE_ALLOC_COSTLY_ORDER)
> - max_retries /= 4;
> - if (*compaction_retries <= max_retries) {
> - ret = true;
> - goto out;
> - }
> -
> - /*
> - * Make sure there are attempts at the highest priority if we exhausted
> - * all retries or failed at the lower priorities.
> + * Compaction failed. Retry with increasing priority.
> */
> -check_priority:
> min_priority = (order > PAGE_ALLOC_COSTLY_ORDER) ?
> MIN_COMPACT_COSTLY_PRIORITY : MIN_COMPACT_PRIORITY;
>
